crypto/arc4.c

   1 /*
   2  * Cryptographic API
   3  *
   4  * ARC4 Cipher Algorithm
   5  *
   6  * Jon Oberheide <jon@oberheide.org>
   7  *
   8  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License as published by
  10  * the Free Software Foundation; either version 2 of the License, or
  11  * (at your option) any later version.
  12  *
  13  */
  14 #include <linux/module.h>
  15 #include <linux/init.h>
  16 #include <linux/crypto.h>
  17
  18 #define ARC4_MIN_KEY_SIZE       1
  19 #define ARC4_MAX_KEY_SIZE       256
  20 #define ARC4_BLOCK_SIZE         1
  21
  22 struct arc4_ctx {
  23         u8 S[256];
  24         u8 x, y;
  25 };
  26
  27 static int arc4_set_key(struct crypto_tfm *tfm, const u8 *in_key,
  28                         unsigned int key_len)
  29 {
  30         struct arc4_ctx *ctx = crypto_tfm_ctx(tfm);
  31         int i, j = 0, k = 0;
  32
  33         ctx->x = 1;
  34         ctx->y = 0;
  35
  36         for(i = 0; i < 256; i++)
  37                 ctx->S[i] = i;
  38
  39         for(i = 0; i < 256; i++)
  40         {
  41                 u8 a = ctx->S[i];
  42                 j = (j + in_key[k] + a) & 0xff;
  43                 ctx->S[i] = ctx->S[j];
  44                 ctx->S[j] = a;
  45                 if(++k >= key_len)
  46                         k = 0;
  47         }
  48
  49         return 0;
  50 }
  51
  52 static void arc4_crypt(struct crypto_tfm *tfm, u8 *out, const u8 *in)
  53 {
  54         struct arc4_ctx *ctx = crypto_tfm_ctx(tfm);
  55
  56         u8 *const S = ctx->S;
  57         u8 x = ctx->x;
  58         u8 y = ctx->y;
  59         u8 a, b;
  60
  61         a = S[x];
  62         y = (y + a) & 0xff;
  63         b = S[y];
  64         S[x] = b;
  65         S[y] = a;
  66         x = (x + 1) & 0xff;
  67         *out++ = *in ^ S[(a + b) & 0xff];
  68
  69         ctx->x = x;
  70         ctx->y = y;
  71 }
  72
  73 static struct crypto_alg arc4_alg = {
  74         .cra_name               =       "arc4",
  75         .cra_flags              =       CRYPTO_ALG_TYPE_CIPHER,
  76         .cra_blocksize          =       ARC4_BLOCK_SIZE,
  77         .cra_ctxsize            =       sizeof(struct arc4_ctx),
  78         .cra_module             =       THIS_MODULE,
  79         .cra_list               =       LIST_HEAD_INIT(arc4_alg.cra_list),
  80         .cra_u                  =       { .cipher = {
  81         .cia_min_keysize        =       ARC4_MIN_KEY_SIZE,
  82         .cia_max_keysize        =       ARC4_MAX_KEY_SIZE,
  83         .cia_setkey             =       arc4_set_key,
  84         .cia_encrypt            =       arc4_crypt,
  85         .cia_decrypt            =       arc4_crypt } }
  86 };
  87
  88 static int __init arc4_init(void)
  89 {
  90         return crypto_register_alg(&arc4_alg);
  91 }
  92
  93
  94 static void __exit arc4_exit(void)
  95 {
  96         crypto_unregister_alg(&arc4_alg);
  97 }
  98
  99 module_init(arc4_init);
 100 module_exit(arc4_exit);
 101
 102 MODULE_LICENSE("GPL");
 103 MODULE_DESCRIPTION("ARC4 Cipher Algorithm");
 104 MODULE_AUTHOR("Jon Oberheide <jon@oberheide.org>");